Capillary baffle-constant oil height independent of oil level

ABSTRACT

Apparatus for applying offset-preventing liquid to a fuser roll structure incorporated in a xerographic reproducing apparatus. The apparatus for applying the liquid comprises an applicator roll for providing a film of liquid to a wick assembly having a fluorocarbon polymer fiber layer contacting the fuser roll structure and a capillary forming member cooperating with the applicator roll to convey liquid from a sump area to parts of the applicator roll remote from the sump.

1 51 May 20, 1975 United States Patent 11 1 Thettu UU an 66 hh TT [73] Assignee: Xerox Corporation, Stamford, Primary EXllmi'1erMeTVifl Stein Conn. Assistant ExaminerDouglas Salser [57] ABSTRACT Apparatus for applying offset-preventing liquid to a fuser roll structure incorporated in a xerographic re- [22] Filed: Dec. 26, 1973 [21] Appl. No.: 427,750

52 us. 118/261; 432/60 producing apparatus The apparatus for applying the B059 11/105 liquid comprises an applicator roll for providing a film [51] Int.

of liquid to a wick assembly having a fluorocarbon polymer fiber layer contacting the fuser roll structure 2 B3 00M H00 h C r a e and a capillary forming member cooperating with the- 1 References Clted applicator roll to convey liquid from a sump area to UNITED STATES PATENTS parts of the applicator roll remote from the sump.

2,325,129 7/1943 118/401 2,369,769 2/1945 118/401 8 Clams 3 D'awmg guns PATENTEU HAYZO 19. 5

SHEET 10F 3 PATENIEB HAY 2 01975 SHEET 2 BF 3 CAPILLARY BAFFLE-CONSTANT OIL HEIGHT INDEPENDENT OF OIL LEVEL BACKGROUND OF THE INVENTION This invention relates, in general. to contact fusing systems and more particularly to improved means for applying offset-preventing liquid to the heated fuser member of a contact fusing system.

In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual image can be either fixed directly upon the photosensitive member or transferred from the member to a sheet of plain paper with subsequent affixing of the image thereto. The fixing can be effected by the utilization of heat and pressure.

In order to permanently affix or fuse electroscopic toner material onto a support member by heat and pressure, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This action causes the toner to be absorbed to some extent into the fibers of the support member which, in many instances, constitutes plain paper. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be firmly bonded to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member is old and wellknown. It will be appreciated that the images can be formed by other than electrostatic methods.

One approach to thermal fusing of electroscopic toner images onto a support has been to pass the support with the toner images thereon between a pair of opposed toner members, at least one of which is internally heated. During operation ofa fusing system of this type. the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll to thereby effect heating of the toner images within the nip. By controlling the heat transferred to the toner, virtually no offset of the toner parti cles from the copy sheet to the fuser roll is experienced under normal conditions. This is because the heat applied to the surface of the roller is insufficient to raise the temperature of the surface of the roller above the hot offset temperature of the toner whereat the toner particles in the image areas of the toner would liquify and cause a splitting action in the molten toner to thereby result in hot offset." Splitting occurs when the cohesive forces holding the viscous toner mass together are less than the adhesive forces tending to offset it to a contacting surface such as a fuser roll.

Occasionally. however, toner particles will be offset to the fuser roll by an insufficient application of heat to the surface thereof ((i.e., cold offsetting); by imperfections in the properties of the surface of the roll; or by the toner particles insufficiently adhering to the copy sheet by the electrostatic forces which normally hold them there. In such a case, toner particles may be transferred to the surface of the fuser roll with subsequent transfer to the backup roll during periods of time when no copy paper is in the nip.

Moreover, toner particles can be picked up by the fuser and/or backup roll during fusing of duplex copies or simply from the surroundings of the reproducing apparatus.

One arrangement for minimizing the foregoing problems, particularly that which is commonly referred to as offsetting has been to provide a fuser roll with an outer surface or covering or polytetrafluoroethylene, commonly known as Teflon, to which a release agent such as silicone oil is applied, the thickness of the Teflon being on the order of several mils and the thickness of the oil being less than I micron. Silicone based oils, which possess a relatively low surface energy, have been found to be materials that are suitable for use in the heated fuser roll environment where Teflon constitutes the outer surface of the fuser roll. In practice, a thin layer of silicone oil is continuously applied to the surface of the heated roll to thereby form an interface between the roll surface and the toner images carried on the support material. Thus a low surface energy layer is presented to the toner as it passes through the fuser nip and thereby prevents toner from offsetting to the fuser roll surface. A fuser roll construction of the type described above is fabricated by applying in any suitable manner a solid layer of adhesive material to a rigid core or substrate, such as the solid Teflon outer surface or covering of the aforementioned arrangement.

A wick has been employed to dispense silicone oil on the outer surface of the fuser member. Where the heated member is disposed below its cooperating backup member it is necessary to provide structure for conveying of said offset-preventing silicone oil against the forces of gravity. To this end, a rotating applicator roll in combination with an auxiliary wick has been employed. In order to obtain satisfactory operation with such an arrangement, it is necessary to prevent compaction of the auxiliary wick material against the applicator roll and to prevent the fibers of the wick from contaminating the roll.

Accordingly, it is the primary object of this invention to provide a new and improved pressure and heat fusing system.

It is a more particular object of this invention to provide a new and improved roll contact fusing system and structure for applying offset-preventing liquid to the heated member of the Contact fusing system.

Another object of this invention is to provide an improved structure for applying offset-preventing liquid to a heated fuser member which minimizes problems of installation and insures operation of the fuser with a minimum of maintenance.

BRIEF SUMMARY OF THE INVENTION Briefly, the above-cited objects are accomplished by the provision of structure for applying offsetpreventing liquid to a heated fuser member which comprises a wick member contacting the heated member in combination with a roll applicator capable of rotating through a sump of offset-preventng liquid and conveying the same to the wick. A baffle member is provided which during shorter operating runs of the fuser conveys the liquid from the sump to the applicator roll to an area remote from the liquid and adjacent the wick contacting the heated fuser member. The liquid may also be conveyed by the baffle member to the wick.

The baffle member is provided with ridges serving as standoffs for spacing the baffle from the applicator roll such that they cooperate to form a capillary which serves to convey the liquid.

Further objects of this invention together with additional features and advantages thereof will become apparent from the following detailed description of the preferred embodiment of the invention when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic representation of an automatic xerographic reproducing machine incorporating the heated pressure fusing system utilizing the improved applicating assembly of the present invention;

. FIG. 2 is a side elevation view of the heated pressure fusing system representing the invention; and

FIG. 3 is a partial front elevational view of a baffle member forming a part of the structure for applying offset preventing liquid to a heated fuser member forming a part of the machine illustrated in FIG. 1.

Referring now to the drawings, FIG. 1 illustrates an embodiment of the invention in a suitable environment such as an automatic xerographic reproducing machine. The automatic xerographic reproducing machine includes a xerographic plate or surface formed in the shape of a drum. The plate has a photoconductive layer or light sensitive surface on a conductive backing journaled in a frame to rotate in a direction indicated by the arrow. The rotation will cause the plate surface to sequentially pass a series of xerographic processing stations.

For purposes of the present disclosure, the several xerographic processing stations in the path of movement of the plate surface may be desired functionally as follows:

a charging station A where a uniformelectrostatic charge is deposited onto the photoconductive plate;

an exposure station B at which light or radiation pattern of documents to be reproduced is projected onto the plate surface to dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the documents to be reproduced;

a developing station C at which xergraphic developing material including toner particles having an electrostatic charge opposite to that of the latent electrostatic image is cascaded over the latent electrostatic image to form a powdered image in configuration of the document being reproduced;

a transfer station D where the powdered image is electrostatically transferred from the plate surface to a transfer material such as paper which is then passed through a heated pressure fusing system according to the present invention as will be described hereinafter; and

a drum cleaning and discharge station E at which the plate surface is brushed to remove residual toner particles remaining thereon after image transfer and at which the plate is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic image remaining thereon.

For further details of the xerographic processing stations above, reference is made to copending application Ser. No. 838,902, filed July 3, 1969 now U.S. Pat. No. 3,578,859, issued May 18, 1971.

Referring now in particular to FIG. 2 there is shown the heated pressure fusing system of the present invention which includes a heated fuser roll 16 and a backup pressure roll 18. Fuser roll 16 is a hollow circular cylinder with a metallic core 20 and a polytetrafluoroethylene layer 22. A quartz lamp 24 serves as a source of thermal energy and is located at the center of the fuser roll. Power to the lamp is controlled by a thermal sensor generally called a thermister contacting the periphery of the fuser roll as described, for example, in U.S. Pat. No. 3,357,249. The backup roll 18 is also a circular cylinder and is made up of a metal core surrounded by a thick rubber layer 32 and also a polytetrafluoroethylene layer 34 to prevent silicone oil impregnating the rubber layer 32 and subsequent swelling.

When the two rollers 16 and 18 are engaged as shown in FIG. 2 the applied load deforms the rubber in the pressure roll to provide a nip with a finite width. The copy sheet 40 electrostatically bearing the toner images 42 on the underside is moved through the nip of the rolls with the toner image contacting the fuser roll 16. For a given temperature of the fuser roll, the fusing rate will depend upon the contact arc length of the support material and the dwell time, i.e., the time the toner images remain between the fuser roll 16 and the backup roll 18. Dwell time can be varied either by changing the surface velocity of the rolls or by varying the contact arc length and holding the speed of the roll the same. Contact arc length depends on the softness of the rubber on backup roll 18 and on the amount of pressure between the rolls 16 and 18. The mechanism for driving the rolls and for lowering and raising the rolls into contact can be accomplished by any suitable means as that described for example, in U.S. Pat. No. 3,291,466 or by a suitable mechanical camming device.

As a sheet of material is advanced between the rolls 16 and 18, the toner images on the support material will contact the peripheral heated surface of the roll 16 whereby the toner images become tackified and in this tackified condition the toner will tend to offset on this roll except that it is partially prevented from doing so by the Teflon coating on the roll. However, the applicator or dispensing apparatus of the present invention which applies a thin film of offset-preventing liquid such as silicone oil to the Teflon surface 22 of the fuser roll 16 such that toner offset is prevented as will be described hereinafter.

An oil dispensing apparatus 45 includes wicking assembly 48, an oil pan 50 for maintaining a supply of silicone oil 51 and an applicator roll 52. The oil pan is loaded against the heated fuser roll 16 by a spring action mounting (not shown) as details of the mounting form no part of the present invention. Applicator roll 52 is used to convey a thin film of oil to the bottom face 55 of the wicking assembly as the applicatorroll is rotated in the direction shown by the arrow. Desirably, the applicator roll 52 is driven by an oil dispensing motor 58 which is energized during the fusing operation for a period depending upon the number of copies being produced.

The oil applicator of the present invention utilizes a baffle which may be made from a suitable high temperature (i.e. 400F) resistant material which is impervious to the silicone oil. Typical materials are polyamide polymer known as Kapton, a trademark of E. I. Dupont de Nemours and Company and fiuorinated ethylene propylene or various metals, for example, steel which is coated with the foregoing materials. The baffle 75 is crescent-shaped and has on the inner surface thereof a plurality of helical ridges 76 which are preferably 0.0020.003 of an inch high, 0.0100.015 of an inch wide, and have a pitch therebetween on the order of /2 inch to 1 inch. The foregoing parameters may be varied in accordance with the specific requirements of the system where the baffle is employed.

A steel rod 77 having a diameter of one-eighth of an inch is attached to the lower end of the baffle by any suitable means, for example, by adhesives or by spring clips. The rod is secured in place by a support member 78 and a holding member 80 located adjacent to the bottom of the oil pan or sump 50. The baffle so mounted is disposed contiguous the roll 52 such that the ridges 76 contact the surface of the roll.

In order to insure intimate contact between the roll and the ridges, the distance between the ends of the baffle in an unstressed condition is somewhat less than the chordal distance of the cylinder extending between the ends of the baffle when the baffle is installed.

During operation, lOOcs. silicon oil is conveyed to the top of the baffle over the surface of the applicator roll through the space formed between the baffle and the roll by the ridges. The ridges extend at angles relative to the circumferential extent of the baffle and thereby form a helical pattern which distributes the wear over an area rather than over a single ridge which would be the case if the ridges extended along the circumferential extent of the baffle. It has been found that this baffle arrangement is useful during short operation runs when rotation of the applicator roll 52 is small and oil to the wick 48 must be supplemented to equalize the amount supplied during a much longer run. Thus, in the case of a long run, the oil will be primarily supplied by the applicator roll due to a lag in the capillary action between the baffle and the applicator roll. But during shorter runs or even a single run, the oil dispensing level is increased due to the oil coated onto the applicator roll surface adjacent the wick.

By the above invention it has been found that the baffle not only provides the advantages described above but additionally minimizes any variation in the oil film being dispensed due to changes in the oil level in the oil pan or to the length of operation runs of the machine. Specifically, due to the configuration of the baffle arranged around the applicator roll, to form a capillary, the uniform amount of oil is continuously supplied to the heated fuser roll member irrespective of changes of the oil level in the sump or operational runs.

While the present invention has been disclosed with respect to a preferred embodiment, it is not intended to be limited thereby but is intended to be covered broadly within the scope of the appended claims as limited by the prior art.

What is claimed is:

1. Apparatus for fusing toner images to a substrate by heat and pressure, said apparatus comprising:

a heated fuser member for softening said toner images;

a backup member forming a nip with said heated member through which said substrate moves with said toner images contacting said heated fuser member;

a sump containing a quantity of offset-preventing liquid;

means contacting said heated fuser member for metering a thin coating of offset-preventing liquid thereto;

applicator means adapted to contact said offsetpreventing liquid and conveying it to said means contacting said heated fuser member; and

means for conveying offset-preventing liquid from said sump to the surface of said applicator means at points remote from said sump of offsetpreventing liquid, said conveying means comprising means cooperating with said applicator means to form a capillary therewith, said liquid being conveyed to said applicator at points intermediate said means contacting said fuser member and said sump, said conveying means being impervious to said offset preventing liquid.

2. Apparatus according to claim 1, wherein said applicator means comprises a cylinder and said means cooperating therewith comprises a crescent-shaped baffle supported at one end in said sump whereby the lower end of said baffle is immersed in said liquid.

3. Apparatus according to claim 2, wherein said crescent-shaped baffle has a plurality of ridges serving as standoffs for the baffle.

4. Apparatus according to claim 3 wherein said ridges are on the order of 2 mils in height to provide a 2 mil spacing between the baffle surface and the applicator surface.

5. Apparatus according to claim 3, wherein said ridges form angles with circumferential lines of said crescentshaped baffle.

6. Apparatus according to claim 2, wherein said crescent-shaped baffle is fabricated from a polyimide polymer.

7. Apparatus according to claim 2, wherein said crescent-shaped baffle is fabricated from a fiuocarbon polymer.

8. Apparatus according to claim 2, wherein said crescent-shaped baffle has a non-stressed distance between its ends which is less than the chordal distance between the points of contact of said ends with said cylinder when said baffle is installed whereby said baffle is under tension when installed. 

1. Apparatus for fusing toner images to a substrate by heat and pressure, said apparatus comprising: a heated fuser member for softening said toner images; a backup member forming a nip with said heated member through which said substrate moves with said toner images contacting said heated fuser member; a sump containing a quantity of offset-preventing liquid; means contacting said heated fuser member for metering a thin coating of offset-preventing liquid thereto; applicator means adapted to contact said offset-preventing liquid and conveying it to said means contacting said heated fuser member; and means for conveying offset-preventing liquid from said sump to the surface of said applicator means at points remote from said sump of offset-preventing liquid, said conveying means comprising means cooperating with said applicator means to form a capillary therewith, said liquid being conveyed to said applicator at points intermediate said means contacting said fuser member and said sump, said conveying means being impervious to said offset preventing liquid.
 2. Apparatus according to claim 1, wherein said applicator means comprises a cylinder and said means cooperating therewith comprises a crescent-shaped baffle supported at one end in said sump whereby the lower end of said baffle is immersed in said liquid.
 3. Apparatus according to claim 2, wherein said crescent-shaped baffle has a plurality of ridges serving as standoffs for the baffle.
 4. Apparatus according to claim 3 wherein said ridges are on the order of 2 mils in height to provide a 2 mil spacing between the baffle surface and the applicator surface.
 5. Apparatus according to claim 3, wherein said ridges form angles with circumferential lines of said crescentshaped baffle.
 6. Apparatus according to claim 2, wherein said crescent-shaped baffle is fabricated from a polyimide polymer.
 7. Apparatus according to claim 2, wherein said crescent-shaped baffle is fabricated from a fluocarbon polymer.
 8. Apparatus according to claim 2, wherein said crescent-shaped baffle has a non-stressed distance between its ends which is less than the chordal distance between the points of contact of said ends with said cylinder when said baffle is installed whereby said baffle is under tension when installed. 